libcamera: buffer: Move captured metadata to FrameMetadata

Move the metadata retrieved when dequeuing a V4L2 buffer into a
FrameMetadata object. This is done as a step to migrate to the
FrameBuffer interface as the functions added to Buffer around
FrameMetadata match the ones in FrameBuffer.

Signed-off-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

src/cam/buffer_writer.cpp

@@ -33,7 +33,7 @@ int BufferWriter::write(Buffer *buffer, const std::string &streamName)
 	if (pos != std::string::npos) {
 		std::stringstream ss;
 		ss << streamName << "-" << std::setw(6)
-		   << std::setfill('0') << buffer->sequence();
+		   << std::setfill('0') << buffer->metadata().sequence;
 		filename.replace(pos, 1, ss.str());
 	}